This invention relates to guide members located in the path of a magnetic tape within a magnetic tape cassette.
The term "guide members" as used herein is intended to embrace various types of guide pins, guide ribs, and other members with which the tape runs in sliding contact. Thus, the present invention is extensively applicable to the tape cassettes including video and audio tape cassettes of the type having a magnetic tape which is driven from reel to reel as it is fed and taken up and also having guide members with which the tape runs in sliding contact.
Video cassettes have tape guide members, commonly in the form of hollow posts, usually located at key points within the cassette housing to impart appropriate friction characteristics to the tape during its running. In general, guide members of this character are made primarily of metallic materials. Since the handling of magnetic tape can lead to the buildup of a static charge, the tape guide members are often fabricated from nonmagnetic stainless steels. Where such metals are used, the tape-contacting surface of the parts must be smoothened by plating, polishing, lapping, or other finish to properly reduce the friction with the running tape and avoid damaging of the tape due to the sliding contact. Altogether, these make the guide members expensive. To save the cost, proposals have so far been made to replace the metallic materials by the general purpose resin GP and other resins commonly known as engineering plastics, such as ABS, POM, and PC, filled with various lubricants. However, these substitutes generally show such high rates of molding shrinkage on solidification at the time of injection molding or extrusion that the moldings or extrusions are distorted under strains. Consequently, the resulting guide members are curled or wavy on the surface and, as compared to the members of metallic materials, they are too inferior in smoothness for practical use.